Elastic anisotropy of Ni4Ti3 from first principles

The elastic strain fields surrounding Ni4Ti3 precipitates affect the transformation behavior of Ni-rich NiTi shape memory alloys. We present first-principles calculations of the Ni4Ti3 elastic constants that allow for the first time to characterize the elastic anisotropy, the direction-dependent Young's modulus and the macroscopic elastic moduli. A comparison of the direction-dependent moduli of Ni4Ti3 and the austenitic NiTi matrix fully rationalizes the experimentally observed shapes of the precipitates.